The present invention relates to apparatus and methods for fabricating microelectronic devices, and more particularly, to polishing apparatus and methods.
Fabrication of integrated circuit devices, such as memory devices, microprocessors, and the like, commonly involves the use of chemical mechanical polishing (CMP) to remove materials from a wafer surface and/or to planarize the surface of the wafer before building up additional structures. Generally, CMP involves rubbing the surface of the wafer against a pad made of a resilient material, such as polyurethane, in the presence of a chemical slurry to remove material, such as a metallization layer, deposited on the wafer surface. The pad and/or the slurry may include abrasives.
Several different types of CMP machines have been developed. One type of machine uses a disk-shaped polishing pad that is affixed to a fixed or rotating platen. In such a machine, the wafer is typically supported by a polishing head that rotates the wafer and presses the rotating wafer's surface against the polishing pad.
An example of such a disk-type polishing machine is shown in FIG. 1. The polishing machine 100 includes a polishing head 110, a platen 120, a polishing pad 130 affixed to the platen 120, and a pad conditioner 140. The platen 120 is driven by a motor 150 via a shaft 160. The polishing head 110 is driven by a motor 170 via a shaft 180. The polishing head 110 and the platen 120 may rotate in the same direction or in opposite directions.
FIG. 2 is a cross sectional view of the polishing head 110. The polishing head 110 includes a carrier 111, a manifold 112, a support 113, a retaining ring 114, and a membrane 115. The support 113 includes an inner support 113b and an outer support 113a. The outer support 113a has a generally cylindrical shape with a ring-shaped wall 116 and a protrusion 117. A first fluid path 118 and a second fluid path 119 are configured to carry de-ionized water used to clean the head 110, and to carry air to provide vacuum to pick up wafers and pressure for the polishing process. In particular, the first fluid path 118 and the second fluid path 119 provide pressure at the center area of the wafer and at the edge area of the wafer, respectively, during polishing. First and second holes 121, 122 communicate with the membrane 115. The retaining ring 114 prevents the wafer from slipping out of the polishing head 110.
FIG. 3 shows a typical operation of the polishing machine 100. While holding and rotating a wafer W, the polishing head 110 presses the wafer W against the rotating polishing pad 130. As shown, the polishing head 110 and platen 120 both rotate clockwise. The polishing head 110 may also oscillate in a horizontal plane while holding the wafer against the pad 130, as shown by the double-headed arrow.
A polishing pad may have surface features, such as grooves, that can aid distribution of slurry across the surface of the wafer, as shown in, for example, U.S. Pat. No. 6,561,873 to Tsai et al. Some types of CMP machines impress a spinning wafer against a belt-type polishing pad, as shown, for example, in U.S. Pat. No. 6,634,936 to Jensen et al. and U.S. Pat. No. 6,585,579 to Jensen et al.
Because of the nature of the polishing process, CMP pads wear as they are used. It is generally desirable that wear occur in a uniform manner over the part of the pad that contacts the wafer, such that a substantially uniform polishing profile can be maintained as wafers are polished in the fabrication process. For example, a pad design that tears or develops a significantly non-uniform surface may provide unacceptably non-uniform polishing results or may need to be replaced more often than desired.